This application claims priority under 35 U.S.C. xc2xa7 119(a) from PCT International Application No. PCT/JP99/06042 filed on Oct. 29, 1999, which in turn claims priority from Japanese Application P1998-310633 filed Oct. 30, 1998.
The present invention relates to sputtering apparatus used in fabrication of semiconductor devices and the like.
The sputtering apparatus is such apparatus that the surface of a target being a cathode is bombarded with positive ions of a process gas, normally argon ions, in plasma and that target atoms sputtered therefrom are deposited on a substrate on the anode side, for example, on a semiconductor wafer to form a film thereon.
Such sputtering apparatus commonly employs the so-called magnetron method in order to increase sputter efficiency by increasing the plasma density near the surface of the target. This method uses a magnet device generally called a magnetron system to generate a magnetic field parallel to the surface of the target. Since this magnetic field intersects with the electric field established between the target and the wafer, electrons from the target are captured in the region near the surface of the target, so as to increase the plasma density of that region.
Wiring patterns have been scaled down with recent trend toward higher integration of semiconductor devices and it is becoming difficult to effect efficient deposition in contact holes, via holes, etc. by sputtering. For example, when deposition is implemented over a wafer surface with fine holes in the standard sputtering apparatus, there arises the problem that overhangs are formed at entrances of the holes and degrade the bottom coverage. For this reason, new technology has been developed heretofore, including collimation sputtering, long throw sputtering, and so on.
The collimation sputtering is a technique of placing a plate with many holes called a collimator between the target and the semiconductor wafer and letting the sputtered particles pass through the holes of the collimator so as to provide the inherently non-directional sputtered particles with directivity, thereby mainly depositing only the sputtered particles of the vertical component on the semiconductor wafer.
The long throw sputtering is a method in which the distance between the target and the semiconductor wafer is set considerably longer than that before. In this method, the sputtered particles flying at large angles relative to the semiconductor wafer reach the region outside the semiconductor wafer, so that only the sputtered particles flying in nearly perpendicular directions are deposited on the semiconductor wafer.
The above-stated collimation sputtering and long throw sputtering both are deposition techniques capable of realizing excellent bottom coverage and scale-down of wiring pattern. In the collimation sputtering, however, if the sputtered particles are deposited on the collimator and if the amount of deposition becomes large it can cause plugging and, in turn, lead to degradation of uniformity of deposition and decrease in deposition rate. If a film deposited on the collimator is peeled off, it will be contamination on the semiconductor wafer and be the cause of device failure. Further, the collimation sputtering has another problem that the collimator is heated to high temperatures by the plasma, so as to affect temperature control of the substrate. In addition, since the sputtered particles have the strong straight traveling property, side coverage can be inadequate in some cases.
On the other hand, in the case of the long throw sputtering, since there exists nothing between the target and the semiconductor wafer, there is no need for such a maintenance work as replacement of the collimator, but it has the problem of extremely poor deposition rates, because the distance between the target and the semiconductor wafer is long. In order to assure the vertical deposition of sputtered particles, the discharge voltage needs to be set as low as possible, so as to avoid the sputtered particles from colliding with gas molecules during flight. For this reason, it was necessary to prepare a dedicated magnetron unit in order to enable stable discharge even in a low pressure state, and this was the cause of need for expensive apparatus. Further, there was another problem that deposition rates were different between in the central part and in the peripheral part of the semiconductor wafer and thus uniformity of film thickness was poor across the entire surface of the semiconductor wafer.
There was also such a tendency that erosion occurred greater in the outside part of the target and this posed the problem that the whole target needed to be replaced even with little erosion in the inside part of the target. Arrangement of magnets in the magnetron unit was adjusted in order to uniformize the erosion, but there were various restrictions on the arrangement of magnets. Therefore, there was the problem of incapability of achieving adequate uniformity of erosion.
The present invention has been accomplished under such circumstances and an object of the invention is to provide sputtering apparatus that permits control of directions of deposit-forming particles moving from the target toward the semiconductor wafer, so as to achieve improvement in uniformity of deposition in the surface of the semiconductor wafer.
In order to accomplish the above object, a sputtering apparatus according to the present invention is a sputtering apparatus for depositing a target material on a substrate placed in a process chamber, which comprises a plurality of targets placed opposite the substrate and on a concentric basis in the process chamber, and a means for adjusting sputtering yields of the respective targets.
According to the present invention, the target is divided into a plurality of targets and the sputtering yields are adjusted, for example, by applying different voltages to the respective divisional targets, whereby erosion of each target can be made uniform.
The target placed in the central part can be of either a disk shape or a ring shape.
Further, the present invention is characterized by placement of a shield ring between the targets. This permits plasma to be confined in the space surrounded by the shield ring, which can enhance independence of control of each target and which can restrain the directions of the target particles, thereby enhancing the uniformity of deposition on the surface of the semiconductor wafer.
When the sputtering apparatus of the present invention is provided with a magnetron device, the sputtering yields can also be adjusted by magnets of the magnetron device associated with the respective targets.
The above and other features and advantages of the present invention will become apparent to those skilled in the art by the following detailed description with reference to the accompanying drawings.